Motors and transformers are fabricated undergoing such a process for example as is comprised of the process of inserting a plurality of coils, each of which is formed by winding an insulated wire (enamel wire), into stator slots and then splicing mutually the ends of the plurality of inserted coils by welding or other similar method.
In forming a coil, the insulated wire is wound at a high-speed. Since the high-speed winding in a coil forming process damages the insulated wire leaving scratches on the surface thereof, an insulated wire having excellent coiling properties is required for reduction of such scratches. This means that such an insulated wire as has an improved surface lubricity (self-lubricity) is desired.
There are known methods for improving the surface lubricity of an insulated wire. One of the known methods is applying lubricant on the insulated wire, wherein the major constituent of the lubricant is paraffin, fatty acid ester, or other similar substance. Typical another known method is forming a lubricative layer on the insulated wire. The layer is formed by applying-and-baking insulating coating composition having lubricity on the conductor of the wire, wherein the insulating coating composition is prepared by adding a lubricant, which is similar lubricant to the above-sated composition, to the base resin of the insulating coating composition.
Further another known method is forming a lubricative layer on the insulated wire; the layer is formed by applying-and-baking insulating coating composition having lubricity on the conductor of the wire, wherein the insulating coating composition is prepared by compounding stabilized isocyanate and lubricant into the base resin of the insulating coating composition. (Refer to JP 09-45143 A for example.)
Coils, after being formed by winding insulated wire, are impregnated with varnish, which is then cured to increase mechanical strength and insulating properties. In a coil that uses an insulated wire having a lubricative layer on its outermost surface, the lubricative layer works as a disincentive factor against the adhesion strength (varnish adhesion strength) between the varnish and the coil. Therefore, the varnish adhesion strength in such coil is very low compared with a coil that uses an insulated wire without lubricative layer.
A method of improving this reduction problem of the varnish adhesion strength is the adding of such a composition as is reactive with the varnish to be used for coil impregnation-and-curing (treatment varnish) to the insulating coating composition having lubricity; such reactive substance includes for example epoxy resin, silane coupling agent, and other similar substance. (Refer to JP 2002-75066 A and JP 2007-213908 A for example.)